I2c what is it: https://i2c.info/#:~:text=I2C%20is%20a%20serial%20protocol,almost%20all%20major%20IC%20manufacturers.
simple spec: https://i2c.info/i2c-bus-specification
better spec w samples: http://www.ti.com/lit/an/slva704/slva704.pdf?ts=1590753073878
THE source: https://www.nxp.com/docs/en/application-note/AN10216.pdf